The present invention relates to moisture measuring apparatus and particularly such apparatus for providing accurate measurement in the presence of circuit changes.
Moisture measuring apparatus has been known heretofore for taking moisture measurements by means of a sensor placed in a kiln wherein such sensor is connected to a meter circuit by an intermediate coaxial cable. The sensor would provide a shunting effect on a tuned circuit, according to the extent of moisture present, resulting in a measurement by a meter circuit. Unfortunately, circuits of this type are difficult to maintain in accurately calibrated condition since the presence of moisture is a relatively small parameter compared with other constants of the system. For example, the length of the coaxial cable between the sensor and the meter circuitry would have a pronounced effect on the calibration, and changes in length would require retuning of the circuit. Moreover, changes in circuit constants with age would have an effect on the calibration of the instrument requiring re-zeroing thereof. Generally, such equipment would be supplied with only one length of coaxial cable, although it might be more convenient to employ differing lengths of coaxial cable between the sensor and meter circuitry.